Efficacy of fluvoxamine (FLUV) versus placebo is being assessed in the treatment of children and adolescents with Autistic Disorder (AD). FLUV is a proven effective antidepressant and anti-obsessive-compulsive agent that is a selective serotonin (5-HT) uptake inhibitor. It is the specific effects of this medication on 5-HT that suggest it may be an effective treatment for AD since abnormalities in 5-HT function have been hypothesized to be of etiologic significance in autism.